Control of arcing electrodes



y 1949- w. M. BRUBAKER 2,476,808

CONTROL OF ARCING ELECTRODES Filed Feb. 21 1948 WITNESSES: is, INVENTOR 3 4 M7500 Min/$012:

ATTORN Y Patented July 19, 1949 UNITED STATES PATENT OFFICE CONTROL'OF ARCING ELECTRODES Wilson hi. Brubaker, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 21, 1948, Serial No. 10,027

11 Claims. 1

My invention relates to systems for automatically controlling electrodes of an electric arc, andin particular relates to'a system in which the electrodes. of such an are are first .moved togather-until 'theyzmake contact, .thcnmoved apart ilor a predetermined travel, and then one of the electrodes continuously rotated about its axis asilong as the-arc, continues to burn. Where it is-:desired 'ato operatexan; arc between solid electrodes in a chamber which is; continually evacnated to :a. low pressure the arc, after being struck, .is;;toundito 'be. in a relatively unstable condition in the case of many electrode materials, so that it is necessary to repeatedly restrike it to. produce long continued operation. The present, arrangement. is particularly adapted to thus strike, and when necessary, repeatedly restrike suchan-zarc.

Oneucbiect of my invention is, accordingly, to providenan automatically con-trolled arrangement in which a pair of electrodes between which an arc to be operated are first moved together, then separated fromxeach other by .a 'pred'eter minedtravel, and then one electrode is continuously rotated to insure an even consumption of the electrode material over its surface.

Another object ofv my invention is to provide an arc control "system of the-type which is described, in'which the-restriking of the-arc ispostponed- .fora predetermined interval after it becomes .exti-nguishedwin order to permit the electrodes to cool sufficiently so that theywill not weld together when moved into contact with each other.

Stillianother-object of: my invention is to pro- Vide a .systeminw-hich a pair of arc-electrodes are moved into contact and then out of contactby an electric motor which :is automatically controlled to.-carr-y outsuch movements by :a relay system.

.A.-f.urther objectzof my invention is to provide a-system of control in which a pair of electrodes is, first. moved into :contact and. then moved out of; contact by onemotor controlled automatically inresponse to the electrical condition-of the arc, and then .a second motor is controlled so as to retat-e, one of. the electrodes continuous-1y as long asqthe arc; continues to burn, the last-mentioned motor being thendeen'ergized and the-first-mentioned motor being caused to restr-iket-he are at the end-oi the presentcooling period by'carrying out its above-described sequence of operations again.

A still further objeotof. my-invention is to provide .a motor-control systemwof the nature abovedescribed..-in.which .relays responding to theelectrical .conditionof the are merely control the grid potential of electrical discharge tubes carrying larger currents than the relay contacts to thereby avoid difiiculty from arcing and wear of such contacts.

Other objects of my invention will become apparent upon reading the following description, taken in connection with 'the drawing, in which the single figure is :a schematic circuit diagram showing the motor, relay and control tube connections capable of carrying out my invention.

Referring in detail to the drawing, an upper electrode 1 and a lower electrode 2 of any desired materials are arranged in axial alignment so that their ends can bev moved into contact and separated to draw an electric 'arc'between them. Said are is supplied with. power from a source A inseries with a current flowing relay B having nor mally open contacts closed when current flows from saidusourceA. The electrode 2 is supported by any suitable. arrangement, of which numerous examples are known to men skilled in the art, so that itcaznsbe moved vertically to make contact with the electrode I by rotating a motor armature 3 connected to .it: by a suitable mechanism 4. Rotation ofv the armature 3' in one direction raises the electrode 2 and in the opposite direction. lowers it. The-electrode l is similarly supported so that it can be rotated about its axis by the armature 5 of a turnin motor through a suitable mechanical linkage 6, which is indicated only schematically in: the drawing.

My inyentionrela-tes to the system of electrical control torturn'in'g the armatures 3 and 5 in response to electrical condition in the circuit supplying the electrodes and 2 to carry out in sequence the. operation of moving the electrode 2 upward into contact with electrode I, and then moving it downward for a predetermined travel away from. electrode l; and, upon attainment of this predetermined travel, stopping the armature 3 and starting the armature 5 into rotation to continuously turn the electrode I until current flow throughthe arc ceases. The control system thereupon; after a predeterm'ned interval, again starts-the armature- 3 into rotation to repeat the above' described program of operations whenever thearcgoes out.

Turning in more detail tothe drawing, power foroperation ofthe armatures 3 and 5 and the control system therefor is furnished by a transformer H, having its input terminals connected to an ordinary alternating-current supply line. Asuitablerelay-C which may be connected across the electrodes I: and! ist-arranged to close a pair of contacts I2 to close the circuit from one terminal or the transformer to the upper brushes (as they appear in the drawing) bearing on the commutator of each of the armatures 3 and 5. The lower brush for the armature 3 is connected to the cathode terminal of a grid controlled gaseous discharge tube I3, havin its anode connected to a common bus G running to the other side of the transformer I I, and is also'connected to the plate of tube I6. The lower brush for the armature is connected to the anode of a second grid controlled gaseous electrical discharge tube I4, having its cathode connected to the bus G. The tubes I3, I4 and I6 being unilaterally conductive, it is obvious that the current flowing through armatures 3 and 5 will be direct current, provided (as is herein arranged) that only I3 or I6 is conducting at any time. The field windings associated with the armatures 3 and 5 are connected in series with each other, one terminal thereof bein connected to the bus G and the other terminal being connected to the positive terminal I5 of a direct-current voltage source, having its negative terminal connected to said bus. The anode and cathode of the tube I3 are connected, respectively, to the cathode and anode of a third grid control gaseous discharge tube I6.

In serial relation with the current flowing through the electrodes I and 2, there is provided a current flowing relay B having a pair of contacts I1 which are open when the said current is zero and are maintained closed as long as a comparatively small current flows through said electrodes. The relay contacts I1 are connected to energize the closing winding of a relay [8 which maintains two pairs of contacts I9 and 2I in opencircuit condition as long as the winding it is deenergized, but closes contacts I9 and 2| as long as relay winding I8 is energized.

The contacts I9 are arranged to energize by their closure the actuating winding 22 of a relay 23, having two sets of contacts which are moved from closed to open position when the winding 22 is energized and two additional sets of contacts which are moved from open to closed condition when said winding 22 is energized. The relay 23 and all other relays are shown in the drawing in the condition they stand in when their actuating windings are deenergized. The functions of the sets of contact-s just mentioned will be more fully described later.

The contacts 2I of the relay I8 are arranged to impress, when they are closed, negative voltage derived from a bias voltage source, having a terminal it which is maintained at a negative potential relative to the above-mentioned bus G, upon the control electrode 25 of a double triode tube 26, which has a cathode connected to said bus G and has its anode connected in series with the energizing winding 21 of a relay 28, drawing current for such purposes from the positive terminal I5 above-mentioned. Between the control electrode 25 of the double triode 26 and the common bus is connected a variable capacitor 29 and a variable resistor 3| in multiple with each other. It will be evident from these connections that, when the relay I8 is deenergized, the control electrode 25 acquires the same potential as its associated cathode, i. e., the potential of the common bus; but that as soon as the relay I8 is energized, the contacts 2I are closed to impress across the capacitor 29 a negative potential, and as soon as the Charge is built up sufliciently, the same negative potential is impressed on the control electrode 25 relative to its associated cathode. 0n the other hand, when, at some sub-* sequent time, the relay I8 is deenergized, thereby opening the contacts 2|, the capacitor 29 slowly discharges through the resistor 3| and thereby gradually remove-s the negative potential from the control electrode 25 thus permitting current flow through the winding 21 to begin after a time delay which may be varied at will by adjusting the variable resistor 3| or the variable capacitor 29.

The double triode 26 likewise has a second cathode 32 connected to the common bus through a resistor 33 and has an anode connected to an actuating winding 34 ofa third relay 35, drawing current for this purpose from the positive terminal I5 above-mentioned. Associated with the cathode 32 is a control electrode 36 which is connected to the bus G through a variable resistor 31 shunted by a capacitor 38. The control electrode 36 is likewise connected to a movable switch member 39 in the relay 28 for purposes which will be more fully explained later.

The control electrode of the tube I3 is connected to a movable element II in the relay 21 which is adapted, in the deenergized condition of winding 21, to make contact with a line running to the negative terminal of a bias battery 42 having a positive terminal connected to the cathode of the above-mentioned tube I3. In the energized condition of winding 21, the switch member 4| connects the control electrode of tube I3 to a movable switch member 43 in the relay 23.

The control electrode of the tube I5 is connected to a movable switch member 44 in the relay 35, which switch member in the deenergized condition of the latter relay is connected to a movable member 46 in the relay 23. In the deenergized condition of the winding 22, the movable member 46 is connected to the negative terminal 24 of the bias source above-mentioned by way of a potential divider 20.

The control electrode of the tube I4 is connected to a movable switch member 41 in the relay 35, which switch member in the deenergized condition of the winding 34 of said relay is connected to draw bias from the negative bias terminal 24 above-mentioned.

The movable switch member 46 in the relay 23 is arranged, in the energized condition of the actuating winding 22 of the latter, to make contact with the bus G. The movable switch member 43 in said relay is arranged under the same conditions to make contact with the negative terminal of the bias battery 42. The movable member 39 of the relay 28 is arranged in the energized condition of the actuating winding 21 of the latter to make contact through a potential divider 48 with the negative bias terminal 24 above-mentioned. The movable switch member 4! of the same relay is arranged to make contact with the movable switch member 43 of the relay 23 under the same conditions. The movable member 41 of the relay 35 is arranged to make contact when the actuating winding 34 thereof is energized with the movable switch member 46 of the relay 23, and the movable switch member 44 in relay 35 is arranged to make contact under the same condition with the potential divider 20 above-mentioned.

Such being the electrical connections of the control system for armatures 3 and 5, the mode of operation of the system is as follows.

Starting with the electrodes I and '2 separated from each other, and the primary winding of transformer I I connected to power source appliamm- oation of voltageto electrodes l and 2 f roznpower sourceA causes the closure of the=r-e1a contacts I? to impress the voltage of the=transformer l l on' the} upper brushes of the armatures 3 and 5. Since; in their separated condition, nocurrent will across the gap-between theelectrodes l and the contacts ll of the current flowing relay 3 remain open and the relay- [8 standsde'en'erglued. I he-,-contacts- 2H ofthe latter are thus separated so that nonegative voltage isimprossed from" the biassource 25 onthecontrol electrode-25 m double triodedfi but'that control electrode-has acquired: the potential of its oath-- ode through the previous discharge of capacitor 281 through! resistor 31\ Undersuchconditions, current flow readily takes place between the an and cathode associated-with controll electrode 25; and: actuates winding 211i ofirelay 28 by cur; rent fiow from the positive terminal*- The swltchimembersl 415 and" E 9 of relay 28 thus stand in: respective left-hand:v and? rightehand 130,-; sitions whenever. the input; terminals of trans former lzi are. energized, and stay so as long as no current flowsthrough electnodesl and 2'. The moiiablelswitchmember. 4:! of; relay ZB-is, accords. ingly; heldiinitsleft-hand positionzto connect the ontrol electrode of; thetube i3 to the movable switchmemben 4cm the relays-23.

' By; reason; ofithe fact; that the relay i3; is de mergized; thczcontacts, E9 are open and the ao.. tuating winding 22 of relay 23 is deenergized; thereby leaving the movable switch, member 43 im itsileitg-han'dmosition; to connect it to the cathof; thetube I3 Thus; the control electrode Qif he: t be. I35 is: a th same-- ele tr al: notch ie esi ss athode, e e vs akingit possiblefor ts- 9: Q nduct: cur ent from-the ower armature-igto-the commonbus andthus affording a:.QQmh1ete circuit: for current flounbetweenthe output terminals of the transformer H: through rmatu e 3s i cer-t-hefic dwindin s assoo d- 'd with oth; armatures; 3; and; 5, are always. ener-v sized by; direct, current-irom the 7 positive terminal liietheaarmature .'b8g 'l1SalJQ;tuI1n tomove the electrode 1lsandfirtcwardeachoth r.

The; aboveemcntioned energization of: relay; 2;8 hasmovedz theimovableswitch =member Eti'inthBI'E-c offinto its; rightkhand position, thereby connect-r ing thescontrol electrode 3,,6 inthe double trio-dc 28 tn,the-. potential divider 48; to; impress. a neg-asv tivelvoltagezon the control; electrode 55, thereby preventing; current: flow through; the energizing windingiiidoffrelay35;,toleave themovablc switch members: $41 and; 41]; therein.- in their rightehand positions,- as.shown.- in; the drawing Since the movableswitchmemben ll of: rela 3:5 is inits r-ightrhanda position, current: flow through, the tube l4 and armature 5 is preven-tedJby the fact that:thecontroLelect'rode of tube I l-isconnected tq.d*erivelbias from-.the negative biasterminal 24': Similarly, it will belseen-that, since the. movable switch member 4Q of relay 35c and movable mem-.-; her; of: relay-2:3 are in their right-.handlposia tions; the; control electrode of: tube I6 is connected f to ,t'helnegative potential a divider Zilthere.- bypreventing any: current flow tov armature throughtube l6;

Now, as; soon as the electrodes.- ls and '2 are IBQVfidliIltO contact with each other, current flow from source A. commencing. therethrough will move the contact ll" of the current. flowing relay, Bztogether toenergize thelactuating wind ing-of -relayl I81 This; will: cause immediate closure Qfvthe contacts; land; 2:1. Closureof the Contacts; lit will: energize the actuating winding 6: of= relay-'- 28 to-moveatho movable switchlmembers and lfi thereof respectively to their right-handand left hand positionsl Closure of: th contacts 21: will impress voltage to begin charging thecapacitor 29- negatively and will quickly render the control electrode Min -the-double-triode 26' so neg;- ative in potential that current flow through-tho energizing: winding 2:1 of relay- 28: will becut off;

causing the-movable switch members 39 and 4-! to,

move respectively: to their 1ef=t-hand and right hand positions as they appear inthe drawing? This will: be'lseen to connect thecontrol electrode of tube: l'kimmediately to the negative terminal of bias source 42, thereby cut-ting off-the current fiow through-tube 3 and armaturelwso that fur! ther movement of: the: electrode- 2 by that armature is stopped; The movement of the switching member 46"- to its left-hand position will be seen to disconnect the control electdode of the tube IB fromcontact with-the negative potential diuideu Zl'l and: connect; it to the bus- G t o giveit the same potential as its cathode. Current flow will; accordingly, begin through armature 3"and tube t6, but since the polarity of tube Hvis- 0p-.

posite to-that of tube [3, thedirection or rotattionof=thcarmature-3 will bethe reverse-of-that previously described; and the electrode 2 will accordingly, be moved awayfrom the electrode I thereby-drawing an are between saidelect-rodes;

The. above-mentioned deenergizationof the relay 28-, having caused its switch member-- 39- to move, to the position shownin the drawing, the terminal of capacitor 38 which previouslystood connected 'to a: point of-negativepotentialon-- the potential divider 48 isno'wdisconnected therefrom; The. capaciton so begins to discharge through the resistor 31 at alra-te determined by the resistance thereof, and the-potentiar of control electrode 36 gradually falls to; the potential of its cathode 32-. Thus,- after-a predetermined timedelay, current fiowlbegins-throughthe control-winding 34% of: relay35 to-inove its switch members 44 and 4:1' tottheir left-hand'positions; Such movement of the switch member -44 imme- U diately, causes the control'electrode of tube-I610 derive negative bias; from the negative biasing terminal: 24$ and? therebycuts ofi= current flow through armature It and tube- I6; but it will be noticed;that the resulting cessationoi separatory movement, ofr the electrode Zas aresult of such cessation, of; currentfiow takesplace only after a time; delay. fixed; by the discharge time. of capacitor 38ithroughl resistor-31. Thus,- it. is that the reverse rotationa of. armature 3 has a continued for this; same predetermined time, andlthe length of the are thereby drawn between electrodes- I and 2; 1s similarln-fixed; by the. time constant of the capacitance-resistancecircuit 38, 31;

Movement toward: the left of the movable switch; member. 4:7;- offrela-yl 35-;will: be I seen to 7 disconnect. the. control electrode of tube Hiromthe ne ative bias terminal 24 and to connect it through themovable switch member of relay 2 3; which isalso in it'ssleft-hand position to the busG.which:has'the potential ofthe cathode of tube l41 Current flow through tube- M- and armature 5-thus ispermitted-to begin; thus causing said armature to continuously rotatetheupper electrode l', thereby insuring evenconsumptionlof theielectrodematerial thereof by the arc, However, as previously stated; there is considerable unstability in arcs under certain conditionsof operationandthe current flow through the. arcbetweenelectrodes I and 2*may suddenly 7-5 cease;-. when th-ishappens, the'relay winding l8 is deenergized by the opening of thecontacts ll of the current flowing relay, thereby causing immediate opening of the contacts 19 and 2|. This causes immediate movement of the movable switch members 43 and 46 to their respective left-hand and right-hand position in the drawing. The opening of the contacts 2| will disconnect the control electrode from the negative bias source 24, but since the capacitor 29 is negatively charged, it willmaintain the negative potential on the control electrode 25 for a considerable time, determined by the adjustment of the resistor 3! through which it discharges. Therefore, current flow through actuating winding 2'! of relay 28 remains cut ofi for a time determined by the time constants of the capacitor resistance 29, 3!, and the relay remains in the position shown in the drawing for this predetermined time. Hence the movable switch member 4| continues to connect the control electrode of tube l3 to the negative terminal of bias source 42, thereby preventing current flow through the latter through the armature 3 for the aforesaidpredetermined time. During this same predetermined time, the left-hand position of the switch member 39 of relay 28 maintains the control electrode 36 in tube 26 disconnected from the negative potential divider 48 and current continues to flow in actuating winding 34 to maintain the switch members 44 and 41 of relay 35 in their left-hand position. Howeventhe movement of the switch member 46 in the relay 23 consequent upon the deenergization of the latter will be seen to connect the control electrode of the tube I4 to the negative bias terminal '24, thereby cutting off current flow through tube l4 and stopping rotation of armature 5,

As soon as the capacitor 29 has sufficiently discharged, the potential of control electrode 25 in double triode 26 falls low enough to permit current to begin through winding 21 of relay 28, thereby moving the movable switch members 39 and 4| to their respective right-hand and lefthand positions in the drawing. When the switch member 41 moves to its left-hand position, it will be seen that the control electrode of tube I3 is transferred from contact with the negative terminal of bias source 42 to contact through the switch member 43 in relay 23 with the cathode of tube l3. Thereupon, current flow through armature 3 and tube l3 commences, thus moving the electrodes l and 2 toward each other to restrike the arc; but it will be noted that this movement has begun only after an interval predetermined by the time constants of the capacitor 29 and the resistor 3 I.

Movement of the switch member 39 of relay 28 to its right-hand position thereupon connects the control electrode 36 in double triode 26 to the negative bias source through potential divider 48, thereby cutting off current fio-w through the actuating winding 34 of relay 35, but it will be seen that the resulting movements of the switch members 44 and 41 to their right-hand position merely leaves the control electrodes of tubes l4 and I6 connected to negative voltage points and maintains these tubes in their non-conductive condition.

It will be seen that the entire arc electrode control system has now returned to that condition in which it stood when the motor 3 first began its rotation to move the electrodes l and 2 toward contact with each other. A complete cycle of the program of operation of the apparatus has thus taken place and may be repeated ing of the electrode l by armature 5 takes place only after full separation of the electrodes has been effected and ceases immediately when the arc goes out. These features prevent loss of the electrodes by breakage through freezing together through mechanical movement while they are not sufficiently separated.

It will also be noted that application of voltage to the arc electrodes I and 2 is requisite to.

closure of the contacts 12 which furnish power to the armatures 3 and 5; hence there is no possibility of the armature 3 being energized to move the electrodes 1 and 2 together at a time when no current flow will be present to causev the current-flowing relay B to reverse arma ture 3 and separate the electrodes as soon as they touch. This insures against accidental crushing of the electrodes by improper operationof armature 3.

I claim as my invention:

1. In combination with a pair of electrodes connected to a power source, a motor and means to cause its rotation in one direction to move the electrodes into contact and its rotation in the opposite direction to move said electrodes out of contact, an alternating-current source and a pair of grid-controlled electrical discharge tubes having the cathode of each connected to the anode of the other to control rotation of said motor, means for impressing a negative potential on the control electrodes of both of said tubes while said alternating-current source is deenergized,

F a first relay means energized to remove said negative potential from one said control electrode when said alternating-current source is energized to thereby cause rotation of said motor in one direction, a second relay means responsive to current flow between said electrodes to deenergize said first relay and reapply the last-mentioned negative potential and to remove the neagtive potential on the other said control electrode to thereby cause rotation of said motor in the 0pposite direction, and a time delay to prevent reenergization of said first relay for a predetermined time after cessation of current flow between said electrodes.

2. In combination with a pair of electrodes connected to a power source, a motor and means to cause its rotation in one direction to move the electrodes into contact and its rotation in the opposite direction to move said electrodes out of contact, an alternating-current suorce and a pair of grid-controlled electrical discharge tubes having the cathode of each connected to the anode of the other to control current flow through said electrodes from said power source, means for rendering one of said tubes conductive upon application of voltage to said electrodes, but for rendering it non-conductive when current flows through said electrodes, means for maintaining a negative potential on the control electrode of the other of said tubes while no current flows from said power source through said electrodes but for removing fora predetermined time saidne ative' potential iir response-to current now through said electrodes, a second. motor arranged to impar-t a turning movement. toone of said electrodes; arthilfd grid controlled electricatdischarge tube connecting said second" motorto" a current source, and means for": maintaining said third tubenon-conduct-ive until the lapse of said: predetermined time and? for then rendering said third tube conductive.

3: In: combination with a? pair of: electrodes connected toa power source;,a.motor'and means to" cause its rotation. inones. direction; to: move the electrodes into: contaicti and, its rotation in the opposite direction: to: move: said, electrodes out: of. contact, an" alternating-current source and a pair of grid controlledf electrical discharge tubes: having; the cathode: of each; connected to the anode of; the other" tm control: cur-rent flow through: said electrodes from: said power source, means-for rendering oneof said tubes conductive upon applicationof voltage-to said electrodes, but for rendering it non-conductive, when current flows through said electrodes, means for maintaining a negative potential on the control electrode of the othen'offsaid'tubes-while no current flows from said power source through said electrodes but for removing for a predetermined time said negative potential in response to current flow through said electrodes; a second motor arranged to impart a turning movement to one of saidelectrodes, a third grid-controlled electrical discharge tube connecting said s'econd motor to a current source, means for maintaining said third tube non-"conductive until the lapse of said predetermined time and for then rendering said third tube conductive, and means for maintaining said one of said other tubes non-conductive for a predetermined time after the cessation of current flow between said electrodes.

4. In combination with a pair of electrodes, motor means for moving said electrodes into contact with each other when voltage is impressed on said electrodes but no current flows between them and for then producing a separatory movement between said electrodes in response to current flow between them, means for causing a cessation of movement of said motor means after said separatory movement has continued for a predetermined time, means for then producing another type of movement of one of said electrodes relative to the other said electrode, and means for moving said electrodes again into contact after a predetermined time interval following cessation of said current flow.

5. In combination with a pair of electrodes, motor means for moving said electrodes into contact with each other when voltage is impressed on said electrodes but no current flows between them and for then producing a separatory movement between said electrodes in response to current flow between them, means for causing a cessation of movement of said motor means after said separatory movement has continued for a predetermined time, and means for producing relative rotation of said electrodes only after said sep atory movement ceases, and means for moving said electrodes again into contact after a predetermined time interval following cessation of said current flow.

6. In combination with a pair of electrodes connected to a power source, a motor and means to cause its rotation in one direction to move the electrodes into contact and its rotation in the opposite direction to move said electrodes out of" contact, an alternating-current source and a pair of. grid controlled electrical discharge tubes having the cathode of each connected to the anode of the other to control rotation of said motor, a first relay means energized in absence of currentflowthroughsaid'electrodes to render one of said tubesconducting to rotate said motor in one direction, a second relay responsive to current flow througlr said electrodes to energize the other of said tubes to rotate said motor in the opposite direction upon initiation of current" flow through said electrodes and to deenergize said first relay, and a time delay means to: prevent reenergization of said first relay for a predetermined time after cessation of current flow between said electrodes.

'7'. In combinationwith a pair of electrodes connected to apower-source, a motor and means to cause its rotationin one direction to move the electrodes into contact and its rotation in the opposite direction t'omove said electrodes out or contact, an alternating-current source and a pair of grid-controlled electrical discharge tubes having the cathode of each. connected to the anode of the other tocontrol? rotation of said motor, means for maintaining: a negative potentialonthe control'electrod'es-of both: of said tubes while said alternating current source is deenergized, a first relay means energized to remove said negative potential from one said control electrode when said alt'ernating current source is energized to thereby rotate said motor in one direction, a second relay-means'responsive to. de:- energize said first relay to reapply the lastmentioned negative potential and toremove the negative potential on the other said control electrode to thereby cause rotation of said motor in the opposite direction in response to current flow between said electrodes.

8. In combination with a pair of electrodes connected to a power source, a motor and means to cause its rotation in one direction to move the electrodes into contact and its rotation in the opposite direction to move said electrodes out of contact, an alternating-current source and a pair of grid-controlled electrical discharge tubes having the cathode of each connected to the anode of the other to control rotation of said motor, a first relay means energized in absence of current flow through said electrodes to render one of said tubes conductive to cause rotation of said motor in one direction, a second relay means energized in response to current fiow through said electrodes to deenergize said first relay and to render the other said tube conductive to rotate said motor in the other direction, means for stopping the last-mentioned rotation of said motor after a predetermined time and for energizing a second motor to rotate one of said electrodes, and a time delay to prevent reenergization of said first relay for a predetermined time after cessation of current flow between said electrodes.

9. In combination with a pair of electrodes connected to a power source, a motor and means to cause its rotation in one direction to move the electrodes into contact and its rotation in the opposite direction to move said electrodes out of contact, an alternating-current source and a pair of grid-controlled electrical discharge tubes having the cathode of each connected to the anode of the other to control rotation of said motor, a first relay means which impresses a negative potential on the control electrode of one of said pair of tubes only when said first relay is deenergized thereby permitting current to flow in absence of said negative potential to cause rotation of said motor in one direction, a second relay which impresses a negative potential on the control electrode of the other said tubes only when said second relay is deenergized, means for causing energization of said second relay in response to current flow between said electrodes to deenergize said first relay and to remove said negative potential from the control electrode of said second tube to cause rotation of said motor in the other direction, and a third relay which deenergizes said second relay a predetermined time after initiation of current flow between said electrodes.

10. In combination with a pair of electrodes connected to a power source, a motor and means to cause its rotation in One direction to move the electrodes into contact and its rotation in the opposite direction to move said electrodes out of contact, an alternating-current source and a pair of grid-controlled electrical discharge tubes having the cathode of each connected to the anode of the other to control rotation of said motor, a first relay means which impresses a negative potential on the control electrode of one of said pair of tubes only when said first relay is deenergized thereby permitting current to flow in absence of said negative potential to cause rotation of said motor in one direction, a second relay which impresses a negative potential on the control electrode of the other said tubes only when said second relay is deenergized, means for causing energization of said second relay in response to current flow between said electrodes to deenergize said first relay and to remove said negative potential from the control electrode of said second tube to cause rotation of said motor in the other direction, a third relay which deenergizes said second relay a predetermined time after initiation of current flow between said electrodes, and a time delay to prevent reenergization of said first relay for a predetermined time after cessation of current flow between said electrodes.

11. In combination with a pair of electrodes, motor means for moving said electrodes into contact with each other when voltage is impressed on said electrodes while no current flows between them and for then producing a separatory movement between said electrodes in response to current flow between them, means for causing a cessation of movement of said motor means after said separatory movement has continued for a predetermined time, and means for moving said electrodes again into contact with each other after a predetermined time interval following cessation of said current flow.

WILSON M. BRUBAKER.

REFERENCES CITED The following references are of record in the his of this patent:

UNITED STATES PATENTS Number Name Date 1,313,666 Beck Aug. 19, 1919 2,259,958 Levy Oct. 21, 1941 2,399,388 Reilly Apr. 30, 1946 

